1. Field of the Invention
The present invention pertains to a combination wellbore scratcher and casing centralizer for use with wellbore casings to scratch or clean the wellbore wall free of drilling mud filtercake and to centralize the casing prior to cementing the wellbore annulus.
2. Background
When installing casing in wellbores for oil and gas wells, for example, it is common practice to employ devices known as wellbore scratchers which may comprise plural segments of relatively stiff, flexible wire rope or cable connected to a collar which is disposed around the casing. Other types of scratchers include those with plural wire whiskers which extend radially from a support collar, also disposed on the casing. These "scratchers" are adapted to remove drilling mud filtercake from the wellbore wall during installation of the casing so that a better cement bond is obtained between the wellbore cement and the earth formation when the cementing operation is carried out.
Separate devices known as centralizers are usually used when installing wellbore casings. A common type of centralizer is a collar comprised of longitudinally and radially extending bands or leaf spring like elements. When installed on the wellbore casing at spaced apart points, these devices are operable to centralize the casing in the wellbore to aid in providing uniform wall thickness of the cement which is eventually pumped into the annulus between the casing and the earth formation. Accordingly, plural and different types of devices are usually installed at spaced apart points on a wellbore casing as it is installed in a wellbore to accomplish the centralization and the wellbore wall cleaning or scratching operation. These separate operations which are not always effectively carried out with prior art apparatus are, with the present invention, carried out with a single, unique device which performs dual functions more effectively than many types of prior art devices.